1. Field of the Invention
The invention relates to a copolymer, and in particular to a packaging material utilizing the same and monomers thereof.
2. Description of the Related Art
For light-emitting devices, packaging materials are fairly important. For example, the packaging material used in light-emitting diodes (hereinafter LED) should have several properties such as transparency, thermal resistance, crystallinity, and impact resistance. Polyester is widely used as a packaging material, but still possesses some shortcomings. For instance, poly ethylene terephthalate (hereinafter PET) has a Tg of about 70° C., such that the PET does not meet requirements of high thermal resistance (Tg>100° C.) in LED packaging material. Some related arts replace the monomer terephthalic acid, so-called 1,4-benzenedicarboxylic acid, with 2,6-naphthalenedicarboxylic acid to form poly(ethylene 2,6-naphthalate) (hereinafter PEN) to solve the described problem. The PEN has higher crystallinity than PET and the Tg of PEN achieves 108° C., thereby effectively enhancing the thermal resistance of the packaging material utilizing the same. However, the PEN forms crystalline easily due to its high crystallinity, therefore reducing transparency and being unfavorable to form a molten state using injection packaging. Meanwhile, some related arts blend the previously described two polymers and combine the easier processed, PET and the thermal resistant, PEN. Nevertheless, because the blend standard is not unified and blend properties is easily influenced by polymerizing degree or molar ratio of PET and/or PEN, practical application of the blend confront difficulties such as reproduction and magnification. Thus, designing a novel polymer structure is called for, to combine the advantages of PET and PEN and standardizing packaging material properties.